Textile



TEXTILE FILAMENT ANTI-STATIC GRAFT CU-.

POLYMERS OF ACRYLONITRILE POLYMERS AND SPECIFIC VINYL SULFONIC ACIDS OR WATER-SOLUBLE SALTS THEREOF Richard Nelson Blomberg, Ward, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Dec. 12, 1955, Ser. No. 552,659

5 Claims. (Cl. 8115.5)

This invention relates to a method of improving the static properties of synthetic textile fibers.

The poor electrical conductivity and high dielectric strength of the modern synthetic fibers is well known. As a result, such fibers tend to accumulate electrostatic charges in processing as, for example, in a textile mill or in use as, for example, in a rug. Such charges may be annoying for instance by causing a dress to cling to the body of the wearer, which interferes with the intended hang of the garment; but such properties are worse than annoying in processing, where such static charges, formed through repeated friction of the fiber, may prevent proper spinning, drawing, twisting, winding, weaving or knitting.

Many efforts have been made in the past to alleviate the static properties of such fibers as by treating the spun filaments with a solution or dispersion of an antistatic agent. In general, such attempts have not proved completely satisfactory since the antistatic effect was fugitive to laundering and dry cleaning or in other cases imparted an undesirable property to fiber such as a harsh hand, poor color, or an undesirable odor.

The conductivity of the polymers used for fibers can be increased by the use of copolymers. However, the level of the modifier required for the desired results is so high that the desirable fiber properties of the polymer are drastically reduced. This same objection applies to blends of a conducting substance and a polymer and, in addition, the added substance may be extracted by laundering and dry cleaning.

It is therefore an object of the presentinvention to provide a means of imparting permanent antistatic protection to preformed synthetic fibers. Another object of this invention is to provide a process for polymerizing a monomeric material in the presence of a synthetic fiber made of a polymeric material, in such a fashion that said monomeric material is polymerized and, at the same time is attached or grafted to the synthetic fiber. Other objects will appear in the description that follows.

The objects of this invention have been accomplished by polymerizing an ethylenically unsaturated sulfonic acid or its salt in the presence of a synthetic fiber comprising a homopolymer or copolymer of acrylonitrile.

One manner of testing for static properties is to determine the surface electrical resistivity of a fiber at a given temperature and relative humidity since a low resistance would enable any charges developed to be conducted away. Such resistivity measurements may be made with a megohm bridge (type 544B, General Radio Company), and a probe consisting of two metallic surfaces with a gap of .010 inch which is pressed against the surface of the material being tested by a 300 gram weight. The resistance of cotton thread which is considered to be relatively static free is about 4-6 10 ohms at 72 F. and 63% relative humidity.

Another method of testing the static properties of a yarn is by determining the magnitude of the charge developed in a yarn and how fast a given electrostatic charge on the yarn leaks out. For this purpose an endless belt was formed by plying suflicient strands of the yarn to give 3,123,434 Patented Mar. 3, 1964 2 a total denier of about 400 and then inducing a static charge in it by passing over a grounded aluminum rod of /2 inch diameter. The charge is measured by an electrometer type of detector (model 210, manufactured by Keithley Instruments of Cleveland), modified by the addition of a fan between the yarn and the detector probe and by the addition of an amplifier. The data gives the charge in volts that is developed under standard conditions and the charge decay rate which is related to the time required for V2 of the initial charge to leak off of the strand of filaments after the motion of the endless belt has been stopped.

In the examples, the data given for resistance, charge development, and charge decay rate was obtained by one or more of these methods.

The following examples are given by way of illustration to show the general procedure of accomplishing the invention, but it is to be understood that variations may be made in the percentages, temperatures, catalyst, wetting agent, and reactants. Any of the alkali metal or ammonium salts of ethylenically unsaturated sulfonic acids oro ther sulfoarylethylene acids and their salts may be used as direct substitutes for the potassium pstyrenesulfonate used to illustrate the invention in the examples.

The amount of the potassium styrenesulfonate or one of the equivalents disclosed following the examples may be increased or decreased from the values shown'depending on the results desired, but usually these will be within the range necessary to add a very small amount, sometimes as little as .001%, up to about 10% by weight to the acrylonitrile polymer or copolymer filaments.

Example I An aqueous dispersion of polyacrylonitrile was prepared from 0.10 part potassium persulfate, 2.0 parts sodium lauryl sulfate, 120 parts of water and parts of acrylonitrile. A stainless steel kettle was used, and the free space of the kettle was flushed with nitrogen gas and then sealed. After mixing the contents by relatively mild agitation for 16 to 17 hours at 40 C., the resulting polymer dispersion contained 36% solid material as determined by evaporation of a portion. The aqueous polymer dispersion was diluted with three times its volume of 1% aqueous sodium alginate and extruded through a 20- hole spinneret, the diameter of each hole being .004 inch, into a 2% aqueous solution of calcium thiocyanate. The precipitated filaments traveled 5 inches through the bath and then were passed over a nearly submersed weir into a bath of 58% aqueous calcium thiocyanate at C. The filaments diverged readily and coalesced to a warp of gel filaments in 3 feet of travel. They were washed free from salt in a water bath at 5 C. Finally the filaments were wound at the rate of 8.7 y.p.m. on a bobbin immersed in ice water and stored in a Wet condition.

Fifteen feet of the yarn as produced above was soaked for 10 seconds in a solution of 2 ml. of 60% tertiary butyl hydroperoxide in 50 m1. of water, removed, squeezed to remove excess liquid and then transferred to a solution of A gram of potassium p-styrenesulfonate and A gram of sodium bisulfite in 15 ml. of water for 10 seconds. The yarn was taken out, excess liquid squeezed 05, the yarn rinsed in water and drawn 8 X over a hot pin at- C. The drawn yarn was then scoured in a A percent aqueous solution of sodium lauryl sulfate for 20 minutes, washed with water and the yarn dried. :It was extremely difilcult to induce an electrostatic charge on this yarn at high or low relative humidities by rubbing against rubber, or by usual textile operations, whereas a similar yarn without the added polymerization step readily acquired an appreciable charge upon similar treatment. An infrared spectra of the grafted yarn indicated that between 1% and potassium styrenesulfonate had been chemically attached to the fiber. Mere polymerization on the surface would not have produced this result since the polymeric potassium styrenesulfonate is water soluble and would have been removed in the scouring and washing treatments. Using the same gel yarn as above the procedure was repeated using a,a-azodiisobutyroamidine hydrochloride, cumene hydroperoxide-sodium bisulfite, and hydrogen peroxide-thiourea respectively in place of the tertiary butyl hydroperoxide and NaHSO All these drawn, scoured, and dried yarns displayed significantly lower static than an untreated yarn.

The acrylonitrile in the above polymerization was replaced with 75 parts acrylonitrile and 5 parts of methyl acrylate and the polymerization carried out as before. The dispersion of the resulting acrylonitrile/methyl acrylate (94/6) copolymer was spun in the same manner and the resulting gel yarn treated as before with potassium p-styrenesulfonate and catalyst-activator and drawn. The thoroughly washed and dried yarn that had been submitted to grafting conditions was much less susceptible to acquiring an electrostatic charge than control yarn made of the same polymer and treated in the same manner with the omission of the potassium p-styrenesulfonate and a catalyst-activator system.

Example ll Forty to fifty feet of the yarn prepared in Example I was wound on a bobbin and then treated with the hydroperoxide solution and monomer-sodium bisulfite solution in turn as in Example I. The washed yarn was then drawn 6 X at 100 C. in water, scoured in a detergent, washed in water and dried.

The yarn prepared above had a resistance of X 10 ohms at 65 relative humidity as compared with a resistance of over 1000 X 10 ohms at the same relative humidity of a sample of a control yarn that was prepared in the same manner except for the graft polymerization step.

Measurements on an endless belt of yarn gave the following data:

Relative Half Life of Yarn Humidity, Charge Charge in percent Decay, Volts seconds Grafted Yarn 3g 3 288 Control Item 2 Commercial Polyacrylonitrile 60 300 3:100 Yarn 40 300 4, 000

Example III A solution of polyacrylonitrile in dimethylformamide was dry spun in the conventional manner. As-spun yarn (i.e., the yarn woundup directly from the spinning cell containing about 25% dimethylformamide) was passed at 35 feet per minute over a 1 inch diameter roll which dipped below the surface of a 2% aqueous solution of tertiary butyl hydroperoxide and was immediately carried over a second roll onto which dripped a 0.5% solution of potassium styrenesulfonate containing 0.1% NaHSO The yarn was then passed onto an input roll, heated to about 90 C., and then drawn 4 X by passage over a feed roll, a pin heated to about 150160 C. and a drawing roll in turn. The yarn was scoured minutes in /2% sodium lauryl sulfate at 9095 C. It was then given a wash in cold water and two washes at 80-90 C. followed by a 20-minute wash in distilled water and dried. A control sample was prepared on the same equipment by removing the hydroperoxide and potassium styrenesulfonate baths.

The surface electrical resistivity at 65% relative humidity and 72 F. was between 3 X 10 and 15 X 10 ohms for theformer and from 200 to 1000 X 10 ohms for the control.

Fiber characterization tests show that the potassium styrenesulfonate treatment did not alter the tenacity, initial modulus, ultimate elongation or tensile recovery from 5% elongation. It was surprising that the yarn treated with potassium styrenesulfonate showed a significant increase in abrasion resistance to the control as measured on the Stoll tester.

-An aqueous dye bath was prepared containing 2% of the basic dye CI No. 657 (Victoria Green). The ratio of the bath weight to fiber weight was maintained at 40:1. Both the graft polymer yarn and the control were dyed for two hours at 100 C. The grafted yarn dyed to a moderate shade of green while the control yarn was only dyed to a light shade. Microscope examination of cross sections of the above dyed yarns showed that the grafted yarn was dyed in a thin ring (about 0.1 of the diameter of the filaments) while the control yarn was uniformly stained to a visibly lighter shade. This indicates that the grafting had taken place primarily at or near the surface of the yarn where the concentration of sulfonate groups would be of greatest value in dissipating the surface electrostatic charges. Thus 'a given amount of sulfonate groups on or near the surface of a filament obtained by grafting polymerization would give greater static protection than an equal amount of sulfonate groups distributed homogeneously throughout the filament, as for example by copolymerization or blending.

Example IV The graft polymerization procedureof Example I was repeated with the as-spun yarn of Example III. In addition one treatment was made in which the catalyst was eliminated and another in which the potassium styrenesulfonate was omitted. Similarly the baths of monomers and catalyst were replaced with an aqueous solution of polymeric potassium styrenesulfonate. The resistance of the drawn yarns after scouring and drying of the last three items were all about 1000 times greater than the resistance (which was 4-5 X 10 ohms at 63% RH and 72 F.) of the sample which had been exposed to monomer and catalysts.

Example V An acrylonitrile/potassium para styrenesulfonate (/5) copolymer was made as follows: A solution was formed using distilled, deaerated water (1450 parts), potassium p-styrenesulfonate (4 parts), 5% acetic acid (5 parts) and acrylonitrile (96 parts).

The solution was stirred at 40 C. under nitrogen, and to it was added all at once a mixture of potassium peroxydisulfate (3.2 parts), sodium bisulfite (1.6 parts) and distilled water (50 parts).

Polymerization was continued for one hour under ni trogen at 40 C.; the polymer was then filtered, was washed three times with distilled water using 2000 parts of water each time, and dried at 60 C. under vacuum. The yield of polymer was 81.0 parts. Sulphur analysis, making correction for sulphur originating in the catalyst, indicated that the polymer contained approximately 5% of residue derived from potassium p-styrenesulfonate.

The above polymer was dissolved in dimethylformamide and spun into fiber using conventional dry spinning methods. The yarn was washed, drawn 4 X in atmospheric steam and dried.

As-spun yarn of acrylonitrile homopolymer was treated in a skein with potassium p-styrenesulfonate and catalystactivator as in Example I, washed and drawn under similar conditions as above.

Both the yarn from thecopolymer and the grafted yarn were washed, dried and electrical measurements made under similar conditions with results as given below:

Voltage Developed Resistance at 72 F. and 63% RH, ohms Belt of Yarn Yarn 60% R II Grafted Yarn Yarn From Oopolymer Example VI A solution of a copolymer containing 94% acrylonitrile and 6% methyl acrylate was dry-spun as in Example III and the as-spun yarn was divided into skeins of approximately equal weight. Some of the skeins were treated with potassium p-styrenesulfonate and catalyst, drawn, washed and dried as in Example I. The remaining skeins were given the same treatment with the omission of the grafting step. There was no significant weight difference between the treated skeins and the control skeins.

The resistivity of the control skeins were on the average about 100 times greater than the resistivity of the treated skeins under the same conditions. The improved static properties of the treated yarn persisted after a 30-minute soaking in tetrachloroethylene, a type of dry cleaning agent, initially at 120 C.

This invention is equally applicable to homopolymers and to copolymers of acrylonitrile. Such polymers having 70% or more of acrylonitrile are generally used. Higher acrylonitrile content in the polymers; that is, about 85% or more, is preferred for the advantages in textile properties resulting in, as for example, strength, insolubility, sunlight resistance and other characteristics. Monomers that can be used to make copolymers for this invention include acrylic and methacrylic acids, their amide derivatives and esters, methyl vinyl ketone, vinyl halides, vinyl pyridines and many others as discussed in U.S. 2,456,360 (issued to Arnold on December 14, 1948) and in other places.

Although potassium styrenesulfonate (i.e., potassium styrene-4-sulfonate) has been used to illustrate this invention as a grafting monomer, other members of the same class; namely, sulfoarylethylene acids or their salts can be used in this invention in which the sulfonic acid group can be in either the ortho, meta or para position with respect to the vinyl group. The aromatic nucleus may be substituted with other groups in addition to the sulfonic acid groups. For example, theremay be alkyl, alkoxy and similar groups on the nucleus. Specific examples of benzene sulfonic acids which may be used include the following: 2-methyl-4-vinyl-, 3-methyl- 4- vinyl-, 2-methyl-5-vinyl-, 3,5-dimethyl-6-vinyl-, 2,5-dimethyl 4 vinyl-, 2,5-dimethyl-6-vinyl-, 2,3-dimethyl-6- vinyl-, 3,4-dirnethyl-6-vinyl, 2,4-dimethyl-6-vinyl-, 2,3,5- trimethyl-6-vinyl-, 2-ethyl-4-vinyl-, 3-ethyl-4-vinyl-, and many others. In addition allyl or methallyl sulfonic acids or their. salts such as sodium allylsulfonate and sodium methallylsulfonate as described in U.S. 2,601,256 (issued to Bruson on June 27, 1952) can be used. Also the ethenesulfonic acids or their salts such as ammonium ethene sulfonate as described in U.S. 2,300,920 can be used.

As catalyst for the polymerization there can be used any material which yields unstable free radicals under From Continuous I the conditions of the reaction. Preferably, such catalyst will be water soluble. Examples of the catalyst are the azo compounds of the kind disclosed in U.S. 2,471,951, peroxy compounds such as organic peroxides; e.g., benzoyl peroxide, tertiary butyl hydroperoxide, etc., azines, oximes, amine oxides, and persulfates. Redox polymerizations employing oxygen-yielding catalysts in combination' with a reducing agent, such as sodium bi-sulfite, sodium hydrosulfite, etc., may be used with advantage.

The yarn used in this invention should preferably be in a gel or solvent-swollen state and preferably undrawn. One manner of preparing yarn is by dispersion spinning which is defined as the spinning of a composition com prising a mixture of discrete particles of a water-insoluble fiber-forming polymer in an aqueous medium having a minor proportion of a gellable matrix-forming material dissolved therein into a setting medium with subsequent exposure until the matrix-forming material is coagulated and the discrete polymer articles are immobilized by the resultant matrix and finally coalescing the resulting coagulum with a solvent for the film-forming polymer such as a hydrotropic salt solution. The gel fibers, that is, those coalesced fibers that have not been dried, are particularly suitable for use in this invention. This invention can also be used with the yarns, preferably undrawn, obtained by conventional dry and Wet spinning methods and also by the melt-spinning techniques such as disclosed in U.S. 2,706,674 (issued to Rothrock on April 19, 1955).

The invention can be used in a process that is continuous with spinning. When the process is carried out in separate steps from spinning it is preferable that the gel or swollen structure of the yarn obtained from spinning be maintained until the grafting treatment. When theyarn is swollen predominantly with water as is obtained in dispersion spinning or wet spinning the yarn can be stored in sealed packages, humid closet-s, or can be treated with an aqueous solution of a humectant as taught in U.S. 2,558,735 (issued to Cresswell, July 3, 1951) or 2,558,781 (issued to Pollard, July 3, 1951). If the yarn has been obtained by dry or wet spinning it will be swollen by a solvent or plasticizer for the polymer. The.

swollen structure of such yarns can be retained by storage in a sealed container, e.g., a polyethylene bag or in a closet saturated with vapors of the solvent. All such methods permit an indefinite storage period of the yarn before application of this invention.

Although the illustrations of this invention have shown thorough and repeated scourings and washings, such washings are not necessarily an integral part of the process of this invention. The examples were executed in this manner so that the effects of the invention on the yarn would be due to the invention itself and not to any residual monomer, catalyst or other ionic compounds that might be left in an unextracted yarn. The need for a simple washing or a continuous extraction step of the yarn after drawing in the process of this invention will depend upon subsequent processing of the yarn. Preferably, at some step in the process before such yarn is made into articles of manufacture such as clothing, the residual monomer compounds should be removed in order not to place them in contact with the skin of a person.

This invention is of advantage in that it enables a permanent antistatic protection to be given to synthetic fibers without detracting from the desirable physical properties and aesthetic qualities of such fibers. It can ad: vantageously be applied to all manner of synthetic textile fibers and increases the utility of such fibers in commercial textile processing steps such as spinning, winding, twisting, weaving, knitting, etc., and in addition, when are fabricated into woven goods or knitwear reduces the annoying static characteristics of such articles.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

I claim:

1. A textile comprising a filament of a material from the class consisting of homopolymeric acrylonitrile and a copolymer formed from at least 70% acrylonitrile and at least one other copolymerizable unsaturated monomer, the said filament having thermally graft copolymerized to its gel form, substantially at its surface, a static resistant polymer of a monomer of the class consisting of sulfoarylethylene acids, allylsulfonic acid, ethenesulfonic acid, methallylsulfonic acid, and water-soluble salts thereof.

2. The product of claim 1 in which the ethylenically unsaturated sulfonic acid is present in an amount up to about 10% based on the weight of the acrylonitrile polymer.

3. The product of claim 1 in which the acrylonitrile polymer is a homopolymer.

4. The product of claim 1 in which the acrylonitrile polymer is a copolymer.

8 5. The product of claim 1 in which the ethylenically unsaturated sulfonic acid is a polymer of potassium styrenesulfonate.

.References Cited in the file of this patent UNITED STATES PATENTS 2,031,929 Breuers Feb. 25, 1936 2,283,236 Soday May 19, 1942 2,570,094 Bradley Oct. 2, 1951 2,676,896 Cohen Apr. 27, 1954 2,688,008 Chaney Aug. 31, 1954 2,707,709 Buchdahl May 3, 1955 2,723,246 Boyd Nov. 8, 1955 2,794,793 Coover June 4, 1957 2,883,360 Coover Apr. 21, 1959 2,899,262 Stanton Aug. 11, 1959 2,999,056 Tanner Sept. 5, 1961 2,999,772 Burk Sept. 12, 1961 

1. A TEXTILE COMPRISING A FILAMENT OF A MATERIAL FROM THE CLASS CONSISTING OF HOMOPOLYMERIC ACRYLONITRILE AND A COPOLYMER FORMED FROM AT LEAST 70% ACRYLONITRILE AND AT LEAST ONE OTHER COPOLYMERIZABLE UNSATURATED MONOMER, THE SAID FILAMENT HAVING THERMALLY GRAFT COPOLYMERIZED TO ITS GEL FORM, SUBSTANTIALLY AT ITS SURFACE, A STATIC RESISTANT POLYMER OF A MONOMER OF THE CLASS CONSISTING OF SULFOARYLETHYLENE ACIDS, ALLYLSULFONIC ACID, ETHENESULFONIC ACID, METHALLYLSULFONIC ACID, AND WATER-SOLUBLE SALTS THEREOF. 